Aircrete: A Modern Solution for Social Housing

// the building envelope

The full benefits of the SIG I-House System are being realised at Norton Farm, a housing scheme developed for the Bromsgrove District Housing Trust (BDHT) in Bromsgrove. Adopted under the direction of leading housebuilders Barratt Homes, the system has already greatly advanced the build programme, helping the housing trust turn new homes over to residents far sooner than initially anticipated.

The housing scheme, part developed by Barratt Homes and part by David Wilson Homes, contains 316 residential units with a mixture of one, two and three bed homes in terraced, semi-detached and detached form. BDHT will obtain 126 units through a section 106 agreement which includes 46 units that are being developed for shared ownership purposes, with the sale of these units being fed back into the landlord’s affordable home development programme.
In total, 98 of the homes built for BDHT will be constructed using SIG I-House System with the housing trust already pleased with the progress that has been made on site. Calum Walmsley, development manager at BDHT adds, “The original contract was a five-year programme which has been accelerated by the use of the system, which enables us to let the properties sooner to our ever-increasing waiting list”.
Demand for social housing is high, making speed of delivery an essential part of any house building method. The I-House System incorporating Celcon Elements by H+H, is recognised as a Modern Method of Construction (MMC) and a faster way to build traditional homes.
BDHT’s willingness to embrace new technology has been an integral part of the success of the I-House System at Norton Farm. Now a year into the five-year contract, the scheme is expected to be completed by 2020, four years from when works first began.
We’ve been able to advertise properties ahead of the programme and we’ve had a lot of interest from customers both from a sales perspective and also rental, which is great for us,” Mr Walmsley explains.
This revolutionary housebuilding system is one of a number of build types being trialled by Barratt Homes which is keen to experiment with new build methods that deliver faster and more efficient build speeds.
The full system comprises the inner leaves of external cavity walls, floors, lintels, cavity closers, insulation and roof trusses, with the inclusion of soffit and fascia, creating the internal skin of a property, fully wrapped and ready for follow on trades in just one week.
Celcon Elements, H+H’s full storey-height aircrete wall panels, are used on the inner leaf of the cavity walls and for the internal partition walls including separating walls. Where required, standard thin-joint aircrete blocks are used in combination with Celcon Elements, allowing the system to accommodate non-standard details such as bay windows.
Craned into place by a three-man gang and one crane operator from SIG Offsite, the Elements are quickly positioned and fixed using H+H Element Mortar, a fast-setting and very strong thin-layer mortar developed especially for use with Celcon Elements to form a 2mm airtight joint.
Elements are placed onto a bed of mortar on standard foundations. Prefabricated timber I-floor Joist Cassettes are used in conjunction with the system to maintain speed of build. These are also lifted by crane and sit on top of the first lift of Elements. Following a second lift, roofs of either a standard truss roof construction or the ‘Roofspace I-Roof’, a panelised room-in-the-roof system, are installed. The I-Roof is manufactured offsite in a controlled environment making it a faster, cost effective construction.
Designed to match the height of a standard house, the Celcon Elements have a width of 600mm and a thickness of 100mm but can easily be manipulated and cut on site for cases where the Elements are used under windows. This has a knock-on effect, producing less waste and cleaner working environments.
With less man power required on site it has solved one of the critical challenges faced by Barratt Homes in the Midlands, with a shortage of skilled labour creating a delay in construction.
Oliver Novakovic, technical and innovation director at Barratt Homes has been a key influencer in getting the system into the trial phase and is clear on the benefit the system provides over other traditional build methods.
“Steve Cartwright, our construction director in the West Midlands, felt the system would meet the key objectives of the site, which revolved around speed of build and certain labour availability,” says Mr Novakovic.
“We know that we are looking to deliver more homes in a controlled manner – so to do that while taking into account labour issues, we recognise that we will need to have different options for how we deliver homes.”
While different, the build system is still similar enough to traditional build methods that sub-contractors working on site, plumbers, electricians etc. are not hampered by changes to their typical work practices.
The award-winning system is proving popular for its combination of the speed and efficiency of offsite with the familiarity of traditional build. Steve Cartwright adds his observations.
“It’s simply one of the best offsite systems we’ve seen. It’s basically blockwork erected in a different way which gives us flexibility on site. If you require any design alterations while on site, you can treat it like a traditional build – if you need an additional window suddenly, you can do it, whereas with timber frame you can’t alter this due to structural calculations changing,” he explains.

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